William edward ayrton and thomas mather



(No Model.)

W. E.=AYRTON & T. MATHER. SAFETY DEVIGE FOR ELECTROSTATIC MEASURING INSTRUMENTS.

M LM UNITED STATES PATENT OFFICE.

WILLIAM EDWARD AYRTON AND THOMAS MATHER, OF LONDON, ENGLAND.

SAFETY DEVICE FOR ELECTROSTATIC MEASURING- INSTRUMENTS.

SPECIFICATION forming part of Letters Patent No. 516,341, dated March 13, 1894.

Application filed $eptember 7, 1893. Serial No. 484,956. (No model.) Patented in England September 24, 1892, No.17,093.

To all whom it may concern:

Be it known that we, WILLIAM EDWARD AYRTON, residing at 41 Kensington Park Gardens, and THOMAS MATHER, residing at 19 Agamemnon Road,TVest Hampstead, London, England, subjects of the Queen of Great Britain, have invented certain new and useful Iniprovements in Safety Devices for Electrostatic lVIeasuring-Instruments, (for which we have made application for Letters Patent in England, dated September 24, 1892,No.17,093,) of which the following is a specification.

The objects of our improvements are, first, to enable electrostatic measuring instruments to be connected with or disconnected from electric circuits without danger of shock; sec- 0nd, to afford facilities for rapidly inspecting or renewing the safety fuses; and thirdly, to provide a convenient means whereby the working parts of the instrument may be read ily insulated from the terminals of the instrument and subsequently short circuited so as to bring those working parts to the same potential. We attain these objects by the devices shown in the accompanying drawings, which represent ourimprovements as applied to an electrostatic measuring instrument for Voltages of about two or three thousand volts.

Figure 1 shows the general arrangement of safety terminals, fuse holders and insulating and short-circuiting device about half full size. Fig. 2 gives a section taken on the line a, b, Fig. 1; Fig. 3 a section of the safety terminal and fuse-holder to a larger scale, and Fig. 4. an end view of the fuse-holder and its socket.

.Similar letters refer to similar parts in the several views.

We would here point out that where parts are shown in section, the metal parts are indicated by sectional shading in full lines, whereas parts consisting of insulating material are sectioned in dotted lines.

In making our safety terminals T we inclose the whole of the metal parts M of the terminal including the binding screw B, in insulating material, the distance between such metal and any part of the surface of the terminal which can be touched, being greater than the sparking distance (in air) corresponding with the greatest electric pressure the instrument is intended to indicate or register. In connecting such safety terminals with high potential mains, the insulating covering of the connecting wire is removed only from that portion which goes inside the hole in the metal part M Fig. 3, the edge of the covering abutting against the edge of that hole.

In our, electrostatic instruments the case K is efficiently insulated from theworking parts and the terminals T, and it will therefore be readily understood that by the use of our safety terminals connection with or disconnection from the mains may be easily effected without receiving shocks, and that when connected as above described no person can accidentally touch any part of the instrument in metallic connection with those mains.

The combination of safety terminals and fuse holders readily detachable for inspection and renewal of the safety fuses (or cut outs) is clearly shown in Fig. 3, the terminal T being there in one piece with the fuse holder H. The fuse is contained in the fuse-tube F retained in position by the cap .T. One end of F rests in a metal socket U surrounded by a spring V, which spring is fixed to M. By this device fuse-tubes differing appreciably in length may be used and the metallic connection between M and J efficiently maintained. Our improved safety terminal and fuse holder is also well adapted for maintaining good insulation of the parts from the case.

The insulating and shortcircuiting switch acts in combination with the fuse holders in the following manner: On turning the handle E, Fig. 1 from the position shown in full lines to that indicated by dotted lines, the eccentric X (of insulating material) pushes the springs S, S, away from the fuse holder caps J, J",into the position indicated by dotted lines in Fig. 2, thus insulating them and the working parts (inductor and needle) respectively connected with them, from the terminals and fuse holders. On completingthe movement, the metal piece Y connects S and S together, thus shortcircuiting the working parts, so that the zero of the instrument may be tested. In instruments having vertical dials a weight W carried by an arm fixed to the rod R, prevents the switch being left partially on. In other cases springs may be employed to efiect the same purpose. Another important feature of the switch mech anism shown in Figs. 1 and 2 is the fact that when the instrument is being used, the eccentric X iscompletely separated from the springs S, and the insulation of the working parts from the case is in no way impaired.

\Vhat we claim as our invention,and desire to secure by Letters Patent of the United States, is

1. In combination in an electrostatic measuring instrument a safety terminal having the metal parts inclosed in insulating material, safety-fuse holder and an insulating and short-circuiting device.

2. In combination in an electrostatic measuring instrument, a safety terminal made in one with a fuse holder and detachably attached to the instrument, and an insulating and short-circuiting device.

3. In combination in an electrostatic measuring instrument a safety terminal, fuse holder, and an insulating and short-circuiting device co-acting with the fuse holder and arranged to prevent partial connection.

WILLIAM EDWVARD AYRTON. THOMAS MATHER.

Witnesses as to the signature of William Edward Ayrton:

WM. A. ROSENBAUM, FRANK S. OBER. \Vitnesses as to the signature of Thomas Mather:

THOMAS RIDLEY SOWERBUTTS. ROBERT PERCY BRANssoN. 

